1. Technical Field
The present invention relates to providing communications between computing devices. More particularly, some examples of the invention concern using one or more data replication communication links for general communications between computing devices.
2. Description of Related Art
Computing systems often include computing devices located at different sites. Computing devices at separate sites may communicate over one or more different types of networks. As an example, if a user has a primary datacenter and also has a backup datacenter (for disaster recovery or other purposes), the two datacenters typically are connected with a wide area network (WAN) for IP communications, and storage area network (SAN) for storage communications (for example for replicating data). As an example, IP network communications may be used for web browsers, email, databases, banking, and voice over IP.
With regard to backing up data, many business, government, and other types of computer users, update and store data at a primary datacenter site, and maintain a backup copy of the data, called a remote mirror, at a secondary datacenter site that is physically remote from the primary site. The primary site may be called a local site, and the secondary site may be called a remote site. Storing a backup copy of data at a remote site permits recovering data from the remote site in the event of an equipment failure or other disaster, for example a fire or explosion, which damages or destroys data at the local site. Copying data to a remote secondary site as a backup, for disaster recovery, is referred to as data replication, data shadowing, data mirroring, data duplexing, or remote copying.
The International Business Machines (IBM) Peer-to-Peer Remote Copy (PPRC) facility is an example of a synchronous remote data replication system. With PPRC, when a data update is written from an application running on a host at a local site, to a storage device at the local site, a storage controller at the local site stores the update on the storage device at the local site, and also forwards the update to a storage controller at a remote site for storage on a storage device at the remote site.
A SAN used for backing up data to a remote site, or a WAN used for IP communications between sites, may fail. If the WAN fails, IP communications between the sites will not be possible. The IP communications will be nonfunctional even if the SAN is functioning normally. Users have attempted to avoid the loss of IP communications and/or storage communications, by employing redundant IP networks and redundant storage area networks. However, setting up and maintaining backup networks is generally very costly. For example, in a typical disaster recovery system using redundant networks, the networks are the costliest part of the system, and generally amount to 60-80% of the cost, while hardware and software make up only 20-40% of the cost. Consequently, existing techniques for maintaining network availability are generally inadequate.